Projection storage tube



Aug. 30, 1960 Filed July 14, 1959 S. T. SMITH PROJECTION STORAGE TUBE 3 Sheets-Sheet l Eh lh" 5 :3 U 5 LLOO E 5 N a m lu 10 20:

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INVENTOR SIDNEY T. SMITH ATTORNEY Aug. 30, 1960 s. T. SMITH PROJECTION STORAGE TUBE 5 Sheets-Sheet 2 Filed July 14, 1959 mOIlmOIm INVENTOR SIDNEY T. SMITH ATTORN BY 2,951,177 PROJECTION STORAGE TUBE Sidney T. Smith, Springfield, Van, assignor to the United States of America as represented by the Secretary of the Navy Filed July 14, 1959, SenNo. 827,130

4 Claims. c1. 315-12) (Granted under Title 35, US. Code 1952 see. 266) The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

This invention relates in general to cathode ray storage tubes and in particular toa projection storage tube having high resolution and long persistence.

In the field of radar it is becoming increasingly important to have longer persistence and high resolution in radar displays, especially where the radar display has tactical application. Some prior art devices are capable of 100 lines per inch resolution, however, these devices encounter beam spreading between the storage mesh and the high voltage phosphor which effectively lowers the resolution or sharp definition of the display. Other prior devices utilize magnetic imaging of stored write-beam information to provide a desired increase in resolution but such magnetic imaging introduces distortion of the flood-beam collimation as well as deflecting the write-beam. All prior art cathode ray storage tubes having a diameter of the order of four inches or five inches which use screens either for storing information or for other purposes are susceptible to vibration blurs or blemishes in the display which render the display inaccurate in details. The tube of the present invention avoids or eliminates the disadvantages of prior art devices and provides. high resolution magnetic imaging together with near perfect flood-beam collimation.

Accordingly, it is an object of the present invention to provide a storage tube capable of 700lines per inch resolution or more which eliminates or substantially reduces beam spreading between the storage mesh and the highvoltage phosphor.

Another object of this invention is to provide a storage tube capable of high resolution magnetic imaging with substantially reduced or eliminated write-beam deflection and flood-beam collimation distortion.

A further object of the present invention is to provide a high resolution storage tube of substantially reduced diameter the display of which will not be blurred or blemished by normal vibration of the device.

A further object of this invention is to provide a storage tube having approximately 700 lines per inch resolution in which greater ruggedness and less distortion are obtained without reduction in panel display size.

Other objects and advantages of this invention will become apparent upon a careful consideration of the folr, 2,951,177 Patented Aug. 30, 1960 1 inch scanningsupplies a focused write-beam of electrons which scans a storage grid through a flood cathode and a collector. The flood cathode is a .grid having a cold-cathode electron field emitter, coated on the. side facing the storage grid, which provides a field of electrons between it and the storage grid. These flood electrons are focused by the magnetic field at a point near the storage grid surface creating a front of electrons which are collimated by a collector screen and repelled from the storage grid until the write-beam renders the storage grid more positive. Upon incidence .of the write-beamelectrons on the storage grid, the storage insulator struck by the Write-beam becomes more positive permitting some electrons to be attracted through the lattice toward the phosphor on the viewing screen. The electrons proceeding through the storage grid are focused at the viewing screen by the same magnetic field which focused electrons on the hoodcathode side of the storage grid and also the same magnetic field which focused the write-beam. The paths of electrons moving between the storage grid and the phosphor are more divergent than the paths'of electrons proceeding from the flood cathode to the storage grid because of the strong transverse fields at the interstices of the storage grid and the viewing screen. A most important function of the axial magnetic field is to return divergent electrons to focus at the storage grid and the viewing surface, respectively, regardless of variations in divergence and thereby provide a particularly high resolution.

Referring to Fig. 1, beam writing gun 11 including cathode 12 and grid 13 provides a beam of electrons '15 which impinges on storage grid 18 after passing through the interstices of flood cathode 16 and collector screen 17. The beam is controlled by signal source 28. Vertical and horizontal deflection coils 14 are shown as a unit for purposes of simplicity. It will be appreciated that the deflection coils 14 actually are two separate coils producing fields perpendicular to beam 15 and to each other and energized by deflection voltage source 29. Focus coil solenoid 19 produces a magnetic field substantially parallel to the longitudinal axis of envelope 20 and is energized by focus coil voltage source 30. Flood cathode 16 and collector screen 17 are spaced a selected distance 22 apart to provide desired focus of electrons traveling paths 36. Storage grid 18 is spaced a selected distance 23 from phosphor 21 to provide desired focus of electrons traveling paths 37. Lens 25 is positioned to provide a desired enlargement on display surface 2'6 of the image illuminated on phosphor 21.

In Fig. 2, flood cathode 16 is shown coated with cold emitter 33, such as magnesium oxide, while storage grid 18 is shown coated with an insulating material 34 on the side facing collector 17 and flood cathode 16. A line of equipotential near storage grid 18 is indicated at 40. Electrons traveling paths 36 are focused in the area indicated at 32.

Referring to Fig. 3, envelope 20 is shown in isometric view partly in section with a video signal relayed from antenna '64 through T-R box 40, radar receiver 42 and leads 41 to intensity grid 13. Application of the video signal to grid 13 varies the current in beam 15, which, after being deflected vertically and horizontally by' the fields of deflection coils 46 and 43, respectively, strikes the storage surface of storage grid 18 impressing a charge pattern thereon. The current in coils 43 is proportional to the azimuthal motion of antenna 64 which is relayed mechanically through gear assemblies 62 to sweep gen erator 57. Electrical signals corresponding to the meoriginating erase pulse generator 59 and relayed to the grid through leads 49 permitting electrons from the flood cathode to now strike the insulating coating. These flood cathode, or second source, electrons striking the insulating coating charge the particles thereof more negatively so that each pulse erases a portion of the positive charge pattern. Complete erasure is ordinarily accomplished in approximately one antenna scan, however, it can be done in specified time intervals by varying the reptition rate of the erase pulses. The storage grid charge pattern is relayed to phosphor 21 from which an enlarged image is obtained on display surface 26 by lens 25. In the scene depicted a B-scan, indicated at 51, displays targets 52 whose distance from the transmitter is indicated by their height above line 54 and whose azimuth angle is indicated by horizontal displacemen to the right or left of centerline 53.

The high resolution projection storage tube of the present invention operates entirely within an axial magnetic field which is provided by focus coil solenoid 19. A beam of electrons 15 from gun 11 is controlled in direction by deflection coils 14 and is focused by the field of coil 19 to high resolution on storage grid 18. Before reaching grid 18 the beam passes through the interstices of flood cathode 16 and collector screen 17, triggering the cold-cathode emitter coating 33 on the entire surface of the flood cathode into flood emission toward grid 18. Flood cathode 16 is maintained at ground potential and flood emission once started may be continued through: out operation. The flood emission electrons are collimated along paths 36 by the field of coil 19 and through potential changes at collector screen 17 are concentrated in the region indicated at 32 in front of storage grid '18. The concentrated electrons are repelled by -a low voltage maintained at insulation 34 of storage grid 18 but some of these electrons are attracted into the electric field, in-

dicated at 40, through the interstices of grid 18 upon insulation 34 being made less negative when struck 'by electrons in beam 15. Thus, the pattern of charges on surface 34 is transferred to phosphor 21 through a magnetic field which reproduces at 21 the charge pattern impressed at storage grid 18. Paths 37 represent the motion of selected electrons in the magnetic field as well as the return of these electrons to focus at phosphor 2:1.

Distances 22 and 23 are carefully selected to provide the desired concentration of electrons at region .32 and the desired focus at the phosphor. When a relatively great distance 23 is used the phosphor can be operated at a very high potential without voltage breakdown and objectional field emission points.

'Independent focus conditions can be obtained at grid 18 and phosphor 21 by adjusting the write-beam velocity.

at the write-beam cathode 12, by adjusting the collector potential for flood beam focus in region 32, and by adjusting the phosphor potential to focus the image of the charge pattern. The ultimate high resolution obtained on phosphor 21 is a result of simultaneous focusing of small diameter is distinctly advantageous in that, among other results, the blurring or blemishing from vibration of screens and grids as observed in larger tubes is virtually non-existent in the present invention.

In the particular B-scan radar application depicted in Fig. 3 the radar receiver 42 is ready to receive echo signals as soon as a transmitter pulse is turned off. These echo signals are received, detected and amplified in radar receiver 42, and are applied to intensity grid 13 vary; ing the current in electron beam 15in proportion to the strength of the received signal. As beam 15 passes within the influence of deflection coils 43 and 46 it is deflected horizontally and vertically'in accordance with the outputs of sweep generators 57 and 58 which are representativeof the. azimuth and distance of the reflecting object, respectively. The intensity grid variations and horizontal and vertical deflections provide a positive electrical charge pattern which is stored on the storage grid and corresponds to the space relation of the object reflecting radar signals to the radar antenna. Due to the action of flood electrons the positive electrical charge pattern stored on the storage grid appears as a bright; well defined image on the phosphor'surface.

To avoid accumulation of positive charge patterns on the storage grid, erase pulses are applied to the grid to alter the potential of the storage grid surface and allow flood electrons at low velocity to strike the storage surface. The flood electrons charge the storage surface negatively so that when the erase pulse is removed the surface is again negative with respect to the flood cathode. The erase pulse generator 59 supplies a 10 to30 volt pulse of variable width depending upon the amount of erasure needed. The power necessary to provide required deflection may be supplied by a conventional B+ source, for example, a 300-volt power source.

Many modifications and variations of the present invention are possible pursuant to the above teachings- It is 1 therefore to be understood that the practice of this in vention is not limited by the specific examples in the foregoing description and that this invention is only to be limited by the scope of the appended claims.

What is claimed is:

1. A cathode ray storage tube comprising an evacuated envelope with a principal axis having a first electron gun at one end thereof and a luminescent phosphor dis play surface at the other end, said first electron gun dis posed to direct a first electron beam substantially along said axis toward said display surface, pulse means for impressing a pulse on said first electron gun to cont-r01 the density of the electrons in the output of said gun, a flood cathode screen disposed intermediate said first electron gun and said display surface, said flood cathode screen including a second source of electrons adapted to emit toward said display surface, a collector screen disposed intermediate said flood cathode screen and said display surface for attracting the electrons emitted from said second source of electrons of said flood cathode screen, a storage grid disposed intermediate said collec tor screen and said display surface for electrostatically storing information of said first electron beam, said storage grid including an insulating coating on the surface facing said collectorscreen, horizontal deflection means disposed to control the horizontal displacement of said first electron beam, vertical deflection means disposed to control vertical displacement of said first electron beam, electron beam focusing means for establish ing lines of magnetic force through said tube substantially parallel to the principal axis thereof, said focusing means including a solenoid which encompasses the portion of said envelope between said first electron gun and said display surface, first energizing means for energizing said solenoid, second energizing means for maintaining said collector screen at a selected voltage positive with respect to said flood cathode and of suflicient magnitude to attract said electrons from said. second. source 5 through said collector screen, third energizing means for maintaining said storage grid at a selected voltage posifive with respect to said first electron beam and of sufficient magnitude to attract said first electron beam through said flood cathode screen and said collector screen, fourth energizing means for maintaining said display surface at a selected voltage positive with respect to said storage grid and of sufiicient magnitude to attract a portion of the electrons from said second source through said storage grid; said first electron gun, said flood cathode screen, said collector screen and said storage grid disposed at preselected intervals along said axis; said solenoid in said focusing means energized so as to focus said first electron beam at said storage grid, the electrons from said second source substantially at said storage grid and said portion of the electrons from said second source at said display surface; said second energizing means and said third energizing means of sufiicient magnitude to in combination collimate the electrons from said second source and concentrate these electrons in a region substantially adjacent to the surface of said storage grid facing said collector screen.

2. The device claimed in claim 1 wherein means are provided for starting and controlling emission of the electrons from said second source.

3. The device claimed in claim 1 wherein enlarging means including a projection surface are provided for projecting and enlarging the image on said display surface to said projection surface.

4. The device claimed in claim '2 wherein enlarging means including a projection surface are provided for projecting and enlarging the image on said display surface to said projection surface.

Farnsworth July 10, 1956 Smith Feb. 18, 1958 

